Accident Summary
On September 19, 2014, at 1630 eastern daylight time, a float-equipped Cessna 180B (registration N180GK) was substantially damaged during a forced landing near Piscataquis County, Maine. The private pilot and owner, along with a passenger, sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight, which departed Mud Pond, Maine about 1530.
Sequence of Events
The pilot reported that while maneuvering approximately 2,500 feet north of Lake Ross, Maine, he heard a slight squeal from the engine, followed by sputtering. During the subsequent descent from about 1,500 feet, the engine and propeller stopped completely. Determining that the airplane would not reach Lake Ross, the pilot selected an unpaved road in the woods for the forced landing. During the landing, the right wing struck a tree about 60 feet above the ground, and the airplane impacted the road, resulting in substantial damage to the wings, fuselage, and empennage.
Pilot Information
The pilot held a private pilot certificate with ratings for airplane single-engine land and sea. His most recent FAA third-class medical certificate was issued on May 27, 2014. He reported 1,200 total hours of flight experience, with 950 hours in the accident airplane make and model.
Aircraft Information
The Cessna 180B was manufactured in 1959. Its most recent annual inspection was completed on May 24, 2013, at 4,013 total aircraft hours. A Continental O-470K33 remanufactured engine was installed on August 20, 2005, accumulating 605 hours since that date.
Examination and Findings
The wreckage was recovered to a maintenance facility. A cursory examination revealed no external engine damage, but a borescope inspection of the No. 3 cylinder showed a fractured exhaust valve stem and damage to the top of the No. 3 piston. The engine was retained for further examination.
On October 27, 2014, an examination supervised by an FAA inspector at the manufacturer's facility in Mobile, Alabama, found that the crankshaft rotated freely by hand. Removal of the oil sump revealed piston material and the No. 3 exhaust valve head, which was fractured at the stem below the head. Disassembly showed normal wear on all cylinders except the No. 3 cylinder, piston, and exhaust valve. Both magnetos produced spark at all terminal leads.
The fractured exhaust valve head, stem, and rotocoil were submitted for metallurgical examination. The manufacturer's report indicated that the valve fractured at the transition from the stem to the valve head, with post-separation damage. The fracture initiated at the outer surface of the valve stem and grew in fatigue. An NTSB metallurgist reviewed the reports and concurred with the findings.